As a production method of turbine blade, conventionally, a method of producing the turbine blade by shaving it out of a block material has been generally conducted.
However, in case where the turbine blade is shaved out of the block material, a yield of material is very poor, and the yield is about 10% with respect to a finished product.
On the other hand, when producing a turbine blade, it has been also conducted to forge the turbine blade as a single body.
For example, forging a turbine blade as a single body is disclosed in the following Patent Documents 1 and 2.
In a case of forging a turbine blade, there is a problem that although the yield of material is enhanced, a cost for forging dies is incurred.
Moreover, in a case where turbine blades are individually forged as single bodies, the number of processes for forging is increased, and after forging, it takes a lot of troubles and time for machining for finishing the turbine blades into a final shape and size, including setups for the machining.
In the following Patent Document 3, there is disclosed a forging method of simultaneously forging two forging products with a single die.
However, Patent Document 3 is different from the present invention, because it relates to a forging method of a connecting-rod and does not relate to a method of forging two forging products as an integrally connected body.
Patent Document 1: Japanese Patent Publication No. JP-A-2-80149
Patent Document 2: Japanese Patent Publication No. JP-A-63-112039
Patent Document 3: Japanese Patent Publication No. JP-A-3-23026